Poly(trimethylene terephthalate), herein abbreviated 3GT, may be useful in many materials and products in which polyesters are currently used, for example, films, carpet fibers, textile fibers, miscellaneous industrial fibers, containers and packaging. For use in carpet fibers, 3GT may offer advantages because of built-in stain resistance and superior resiliency. See, for example, an article by H. H. Chuah et al., in IFJ (October 1995) on pages 50-52 concerning poly(trimethylene terephthalate) as a new performance carpet fiber.
British Patent 578,097 disclosed the synthesis of poly(trimethylene terephthalate) in 1941. The polymer, however, is not available commercially. There is a lack of published literature on processes for producing the polymer on other than a laboratory scale.
Many of the proposed uses for 3GT require a polymer of relatively high molecular weight. Other polyesters such as poly(ethylene terephthalate), referred to herein as PET or 2GT, have been commercially made by increasing, either in melt and/or solid-state polymerization, the molecular weight of a lower molecular weight polymer, sometimes referred to as a prepolymer or oligomer. In general, melt polymerizations require higher temperatures, which are more likely to cause polymer decomposition and require expensive equipment. Solid-state polymerizations, in contrast, are usually run at somewhat lower temperatures. Solid-state polymerizations can also have the advantage, compared to melt polymerizations, that very high molecular weights, where melt viscosities would be extremely high, are more readily obtained. In commercial use, however, solid-state polymerizations may be relatively slow.
In the case of PET, solid-state polymerizations usually require that lower molecular weight polymer, in the form of particles or pellets, undergo a relatively lengthy crystallization process prior to being polymerized in the solid-state, in order that the particles do not agglomerate in the solid-state reactor. The crystallization process for PET is usually accomplished by annealing the lower molecular weight polymer at an elevated temperature at which the desired crystallization occurs.
Commonly owned U.S. Pat. No. 5,763,104, issued on Jun. 9, 1998, discloses a process for producing poly(trimethylene terephthalate) useful for obtaining higher molecular weight polymer and a novel crystalline form of the polymer.
It is desirable to obtain a higher molecular weight 3GT polymer without having to expose a lower molecular weight 3GT polymer to lengthy and problematic crystallization and annealing steps.